The present invention is drawn generally to the field of acid modified amines for use as chelating agents and coatings. More specifically, the present invention is drawn to siloxane modified derivatives of carboxylic acid substituted amines and the salts thereof.
Ethylenediamine tetraacetic acid (EDTA) and its salts are well known. Ethylenediamine tetraacetic acid is widely employed as a chelating agent for a variety of metal ions. Also, EDTA is quite polar and a rich source of active carboxylic acid functionality. However, EDTA by itself is incapable of bonding to a substrate surface without disrupting the acid functionality necessary for effective chelation.
If an EDTA like moiety, i.e. a carboxylic acid substituted alkyl amine, could be bonded covalently to a substrate surface, it would be possible to take advantage of a number of the beneficial properties of EDTA in a stationary phase. Further, a substrate surface coated with such a compound or a salt thereof would be extremely hydrophilic and wettable. It is therefore desirable to generate functionalized EDTA like compounds that allow chemical interactions with the substrate surface without affecting the acid groups.
The present invention provides novel compounds comprising siloxane modified amines that are substituted with one or more carboxylic acids having 1 to 20 carbon atoms. The compounds may also be prepared as salts using one or more appropriate metal hydroxides. The present invention further provides a method of synthesizing such compounds. Such compounds can be bonded to a number of substrates in a known way to produce a stationary phase having many of the beneficial properties of EDTA and salts thereof.
The novel compounds according to the current invention have a general structure selected from:
S1xe2x80x94X1xe2x80x94Acxe2x80x83xe2x80x83I and
S1xe2x80x94X1xe2x80x94Acxe2x80x94X2xe2x80x94S2xe2x80x83xe2x80x83II
wherein, S1 and S2 are independently a mono, di or tri siloxane, X1 and X2 are independently alkyl, alkenyl or aryl having from 1 to 20 carbon atoms, and Ac is a carboxylic acid substituted amine or a salt thereof.
Siloxane coupling agents are widely known as affective reagents to couple a functional group to a polar substrate such as glass, silica, quartz, inorganic metal oxides, thoria, silicon, alumina, aluminum, iron, zinc, corona or plasma treated plastics and hydroxy functionalized plastics. These siloxane coupling reagents possess one or more alkoxysilyl groups at one end of the molecule and the active functional group at the other end of the molecule. On hydrolysis in aqueous media the alkoxysilyl groups hydrolyze to active silanol groups. These silanol groups readily form covalent bonds to polar substrates. The substrate surface is then functionalized with the active group at the other end of the siloxane molecule. These siloxane coupling agents as both the free alkoxysilyl and bound to the substrate are referred to herein as siloxanes. Siloxanes that are useful according to the current invention have a general structure selected from: 
wherein, R1, R2 and R3 are independently alkyl, alkenyl, aryl or a substrate, and R4 is either X1 or X2, provided that when R1 is bound directly to Si, it is not a substrate and when R3 is bound directly to Si, it is not a substrate. The two embodiments shown provide one or two siloxane functional groups for binding the carboxylic acid modified amine to a substrate. However, it is possible to provide additional siloxane groups as bonding sites.
Further, the amine portion is preferably selected from mono, di, tri and tetra amines having a general structure selected from: 
wherein, Y1 and Y2 are independently X1, X2 or a carboxylic acid or salt thereof having from 1 to 20 carbon atoms, Y3, Y4, Y5 and Y6 are independently a carboxylic acid or salt thereof having from 1 to 20 carbon atoms, and R5, R6 and R7 are independently alkyl, alkenyl or aryl, provided that at least one of Y1 and Y2 is either X1 or X2. In the embodiment where both of Y1 and Y2 are either X1 or X2 the compound is provided with two siloxane bonding sites.
The novel compounds according to the current invention may be synthesized from the corresponding siloxane modified amines having the general structures:
S1xe2x80x94X1xe2x80x94Axe2x80x83xe2x80x83I and
S1xe2x80x94X1xe2x80x94Axe2x80x94X2xe2x80x94S2xe2x80x83xe2x80x83II
wherein, S1 and S2 are independently a mono, di or tri siloxane, X1 and X2 are independently alkyl, alkenyl or aryl having from 1 to 20 carbon atoms, and A is an amine. A solution is prepared of at least one halogenated carboxylic acid having from 1 to 20 carbon atoms. The siloxane modified amine is then added to the solution in a metered fashion. Preferably the halogenated carboxylic acid is added as an aqueous solution. A suitable metal hydroxide may then be added to the combined mixture or solution to generate a metal salt of the carboxylic acid modified amine. The amine is preferably an un-substituted mono, di, tri or tetra amine having a structure selected from: 
wherein, Y1 and Y2 are independently X1, X2 or hydrogen, R5, R6 and R7 are independently alkyl, alkenyl or aryl, and H is hydrogen, provided that at least one of Y1 and Y2 is either X1 or X2.
The siloxane modified carboxylic acid substituted amines according to the current invention can be applied to a number of different substrate surfaces to generate a modified substrate surface. Such modified substrate surfaces have a number of different applications in medical diagnostics, chemical synthesis and analytical chemistry, DNA and Protein immobilization, and metal chelation as well as in the field of electronics. Particularly, application of a salt, preferably a metal salt, of a siloxane modified carboxylic acid substituted amine according to the current invention provides a modified substrate surface that is extremely wettable compared to an unmodified substrate surface. Such properties are very desirable in the electronics industry. The preferred salt for this application is the potassium salt. Although a number of salts effectively produce a wettable surface, the low levels of sodium required for electronics applications make the potassium salt preferable.